Low-loss printed circuit board antenna structure and method of manufacture thereof

ABSTRACT

The present invention provides a method of manufacturing an antenna structure. In one embodiment, the method includes forming an antenna trace on a substrate proximate a ground plane of the substrate. In addition, the method includes creating an insulation region extending through the substrate and located between the antenna trace and the ground plane.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/295,191 entitled “LOW-LOSS PRINTED CIRCUIT ANTENNA,”to Jan Wielsma, filed on Jun. 1, 2001, which is commonly assigned withthe present invention and incorporated herein by reference as ifreproduced herein in its entirety.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention is directed, in general, communicationdevices and, more specifically, to an antenna structure having alow-loss and high efficiency, and a method of manufacture thereof.

BACKGROUND OF THE INVENTION

[0003] Printed circuit boards (PCBs) are the benchmark for mountingelectronic circuit components in today's communications hardware.Conventional PCBs include a rigid substrate to provide support formounting electronic components in communications devices. In addition,conductive materials are plated over such substrates and etched toprovide electrically conductive traces for interconnecting thesecomponents. For many communication devices, an area or a whole layer ofsuch a PCB is often reserved as a ground plane serving as a referenceground for mounted electronic circuitry. Therefore, PCBs may bemanufactured with multiple layers, each interconnected with conductivevias, to further provide electrical connections for complex electroniccircuitry.

[0004] For many communications devices, antennas are typically formed onthe same PCBs, which also carry transmitting and receiving radiofrequency (RF) circuitry. A common technique employed to form antennason PCBs is to simply etch an antenna trace, similar to the tracesmentioned above, having an antenna feeder trace coupled to desiredcomponents on the PCB. Since space is limited in the ever-decreasingsize of today's communications devices, such antenna traces aretypically formed near one or more ground planes formed on the same PCB.In such arrangements, a portion of the PCB substrate, typically the areaof a PCB having the highest density of electromagnetic energy, remainsin between the antenna and the ground plane, leading to antennaefficiency degradation.

[0005] More specifically, as radio signals travel along an antennatrace, a portion of the signals are typically “lost” through energy lossor dissipation in the medium around the antenna trace, especially themedium between the antenna trace and the ground plane. The portion oftotal initial RF signals radiated into the surrounding space determinesthe antenna transmission efficiency (measured in dB) of the antenna. Thesame principle applies for antenna reception. Ideally, a 100% (0.0 dB)efficiency would be achieved if all of the RF signals traveling throughthe antenna were radiated into the surrounding space. However, as may beexpected, the material from which a PCB is constructed has a largeimpact on the percentage of RF signals that are dissipated into PCBmaterial surrounding the antenna structure. So-called “lossy” PCBs, suchas the popular FR-4 PCB, are composed of materials (e.g., fiberglass andepoxy) that dissipate a relatively large amount of the signal. However,because lossy PCBs are both inexpensive to manufacture and process,manufacturers are eager to utilize them in an effort to drive downoverall manufacturing costs. On the other hand, since RF signal lossbecomes more important as transmission frequencies increase, the currenttrend in communications devices from 2.4Ghz to 5GHz technology mayseverely limit all future use of less expensive lossy PCBs.

[0006] Faced with the problem of RF signal dissipation, somemanufacturers have chosen to employ low-loss PCBs, manufactured frommaterials that allow relatively low signal dissipation, in theircommunications devices. Low-loss substrates such as these usually have adielectric loss coefficient (tg(d)) of about 0.01 or less. Examples ofsuch substrates are the Rogers 4000 series, the PTFE, and the GTEK, eachcomposed of special mixtures of materials such as fiberglass, epoxy,Teflon, ceramic, etc. Conventional antenna structures having an antennatrace formed on low-loss substrates usually have an antenna efficiencyof about −0.5 dB or better, which translates into a radiation efficiencyof about 90% or more. The same antenna structure on a lossy PCB, such asFR-4, usually has an antenna efficiency of about −2.0 dB, whichtranslates into a radiation efficiency of about 65%. However, althoughproviding increased antenna efficiency, low-loss PCBs tend to drive upoverall product costs.

[0007] Another approach to reducing signal dissipation, and thusincreasing antenna efficiency, has been to mount antennas above thesubstrate of the PCB. Those who are skilled in the art understand thatair (e.g., an open space) between the antenna and the ground planeprovides an optimum medium for antenna efficiency. The presence ofalmost any material in its place leads to decrease in antennaefficiency. Unfortunately, manufacturing such 3-dimensional antennas onPCBs, even low cost lossy PCBs, typically requires at least some humanintervention during the manufacturing process. Of course, humanintervention into the manufacturing process typically drives up theoverall manufacturing costs of communications devices. In addition,human error that may occur during manufacturing detracts from overallproduct quality and longevity. Materials beyond the etched platedconductors used for antenna traces may further increase overall costs.Moreover, since such raised antennas are typically held on the substrateby a limited number of points, usually only two, the chance for antennabreakage during product use is increased.

[0008] Accordingly, what is needed in the art is an antenna structure,for use with a PCB, that does not suffer the RF signal dissipationexperienced on prior art PCBs.

SUMMARY OF THE INVENTION

[0009] To address the above-discussed deficiencies of the prior art, thepresent invention provides an antenna structure. In one embodiment, theantenna structure includes an antenna trace formed on a substrateproximate a ground plane of the substrate. The antenna structure furtherincludes an insulation region extending through the substrate andlocated between the antenna trace and the ground plane.

[0010] In another embodiment, the present invention provides a method ofmanufacturing an antenna structure. In one embodiment, the methodincludes forming an antenna trace on a substrate proximate a groundplane of the substrate. In addition, the method includes creating aninsulation region extending through the substrate and located betweenthe antenna trace and the ground plane.

[0011] In yet another embodiment, the present invention provides aprinted circuit board (PCB). In one embodiment, the PCB includes asubstrate having a ground plane and conductive traces formed thereon. Inaddition, the PCB includes an antenna structure having an antenna traceformed on the substrate proximate the ground plane. The antennastructure also includes an insulation region extending through thesubstrate and located between the antenna trace and the ground plane.

[0012] The foregoing has outlined preferred and alternative features ofthe present invention so that those skilled in the art may betterunderstand the detailed description of the invention that follows.Additional features of the invention will be described hereinafter thatform the subject of the claims of the invention. Those skilled in theart should appreciate that they can readily use the disclosed conceptionand specific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a more complete understanding of the present invention,reference is now made to the following detailed description taken inconjunction with the accompanying FIGUREs. It is emphasized that variousfeatures may not be drawn to scale. In fact, the dimensions of variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion. In addition, it is emphasized that some circuit componentsmay not be illustrated for clarity of discussion. Reference is now madeto the following descriptions taken in conjunction with the accompanyingdrawings, in which:

[0014]FIG. 1 illustrates one embodiment of a printed circuit board (PCB)having an antenna structure constructed according to the principles ofthe present invention; and

[0015]FIG. 2 illustrates a section side view of a portion of the PCB andantenna structure illustrated in FIG. 1.

DETAILED DESCRIPTION

[0016] Referring initially to FIG. 1, illustrated is one embodiment of aprinted circuit board (PCB) 100 having an antenna structure constructedaccording to the principles of the present invention. The PCB 100includes a substrate 110. In accordance with conventional practice, thesubstrate 110 may be a lossy circuit board, for example, the popular andinexpensive FR-4 board. By employing a relatively high loss board, suchas an FR-4 PCB, the overall manufacturing costs of the PCB 100incorporating the present invention may be kept low. Of course, thepresent invention may be also employed with a low loss PCB withoutdetracting from the benefits described herein.

[0017] Mounted on the substrate 110 is a ground plane 120. As is wellknown, the ground plane 120 provides an electrical ground connectionsfor electrical circuitry 130 located on the substrate 110 and mountedover the ground plane 120. If the PCB 100 includes multiple layers, asis typically the case, the ground plane 120 may occupy several levels ofthe PCB 100, with vias interconnecting the several layers. In addition,the circuitry 130 may include vias and conductive traces (notillustrated) to electrically interconnect various components of thecircuitry 130 to each other and to the ground plane 120. In an exemplaryembodiment, the conductive traces and ground plane 120 are plated copperand are formed on the substrate 110 by etching away unwanted portions ofcopper plating. Of course, other conductive materials may be used toform conductive traces. In addition, other processes for forming theconductive traces over the substrate 110 may also be employed.

[0018] The PCB 100 further includes an antenna feeding line 140. Asillustrated, the antenna feeding line 140 is electrically coupled to thecircuitry 130 located on the substrate 110. In accordance withconventional practice, the antenna feeding line 140 provides aninterconnection between circuitry employing radio frequency (RF) inputand output signals and an antenna structure 150. In the illustratedembodiment, the antenna structure 150 includes an antenna trace 160.Both the antenna feeding line 140 and the antenna trace 160 may beformed on the substrate 110 in a manner similar to that used to formconductive traces, however the present invention is not so limited. Inaddition, the antenna feeding line 140 and the antenna trace 160 may beformed from copper, primarily because of its conductive properties, butthe present invention is broad enough to encompass other materialshaving similar characteristics.

[0019] As is commonly found on conventional circuit boards employing RFcommunications, the antenna trace 160 is formed on the substrate 110 inrelatively close proximity to the ground plane 120. As is known, thematerial comprising the substrate 110 may allow a portion of the RFsignals passing through the antenna trace 160 to dissipate in thesubstrate 110 material, which is the RF signal loss. Circuit boardscomposed of materials that lose a relatively high portion of RF signals,for example, about 35% of signals, through dissipation in the substrate110 are known as high loss or “lossy” PCBs. Such lossy PCBs are commonlyconstructed from a mixture of fiberglass and epoxy, or similarinexpensive materials. Such lossy PCBs typically have a tg(d) of about0.04 or higher, and thus an antenna efficiency of about −2.0 dB orworse.

[0020] In contrast, if the material comprising a PCB only allows arelatively low dissipation of RF signals to the ground plane 120, forexample, less than about 15% of signals, then it is usually known as alow-loss PCB. Such low-loss PCBs are commonly constructed from ceramic,Teflon or even special mixtures of fiberglass and epoxy, and typicallyhave a tg(d) of about 0.01 or lower, and thus an antenna efficiency ofabout −0.5 dB or better. As discussed above, since low-loss PCBs aresignificantly more costly than lossy PCBs, manufacturers have typicallysettled for a decreased antenna efficiency in exchange for lower overallmanufacturing costs. However, a PCB antenna structure according theprinciples disclosed herein allows the use of a less expensive lossyboard, without suffering from the low antenna efficiency traditionallyassociated with lossy PCBs.

[0021] To the accomplish this, the antenna structure 150 of the presentinvention includes an insulation region 170 formed between the groundplane 120 and the antenna trace 160. In the illustrated embodiment, theinsulation region 170 is shown as a plurality of openings (some of whichare designated 180) formed through the substrate 110 and, thus, imposingair as an insulator. However, it must be understood that the presentinvention is not limited to a plurality of openings 180, and is broadenough to encompass other types of insulation barriers. Otherembodiments of the antenna structure 150 may include a solid insulatingmaterial inserted between the ground plane 120 and the antenna trace 160to form the insulation region 170. In such an embodiment, conventionalforms of plastic (for example, ABS plastic) may be used as a solidinsulating material to create the insulation region 170 of the antennastructure 150. Other embodiments may employ conventional low-lossmaterials, such as Teflon or ceramic, as an insulating material in theinsulating region.

[0022] In the illustrated embodiment, when the insulation region 170 isformed with openings 180, all or a substantial portion of the substrate110 originally located between the ground plane 120 and the antennatrace 160 is removed. Since all or a substantial portion of thesubstrate 110 from this location is removed (or replaced if aninsulating material is used), there remains far less material of thelossy substrate 110 through which RF signals may dissipate through tothe ground plane 120. Therefore, the decrease in RF signal loss resultsin an increased antenna transmission and reception efficiency. In thoseembodiments where an insulating material is used to create theinsulation region 170, the RF dissipation properties of the materialwould determine the antenna efficiency.

[0023] In another embodiment, the insulation region 170 is created by asingle opening 180 formed between the ground plane 120 and the antennatrace 160, removing all of the substrate 110 material from thatlocation. In such an embodiment, a portion of material may be left atopposing ends of the antenna trace 160 to provide at least minimalstructural support for the portion of the substrate 110 on which theantenna trace 160 is formed. Additionally, the opening 180 may be madeas large as the area of the substrate 110 between the antenna trace 160and the ground plane 120, and extend to the edges of each. By creatingthe opening 180 as large as possible, less amount of substrate 110material remains in the area of high concentration of RF energy, thusavoiding the dissipation of RF signals into the substrate 110.

[0024] In an advantageous embodiment, multiple openings 180 form theinsulation region 170 by drilling holes through the substrate 110. Inthis embodiment, illustrated in FIG. 1, “bridges” (some of which aredesignated 190) are left between the ground plane 120 and the antennatrace 160. As a result, a substantial portion of the substrate 110material between the ground plane 120 and the antenna trace 160 isremoved, preventing a significant amount of RF signal dissipation in thesubstrate 110. Advantageously, however, structural support is stillprovided by the bridges 190. More specifically, by leaving bridges 190between the ground plane 120 and the antenna trace 160 a strongstructure remains between the portion of the substrate 110 on which theantenna trace 160 is formed and the remaining portions of the substrate110 on which the ground plane 120 is formed. As before, the multipleopenings 180 may also be made as large as the area between the antennatrace 160 and the groung plane 120, extending the length of each, takinginto account the desired size of the bridges 190.

[0025] Turning now to FIG. 2, illustrated is a section side view of aportion of the PCB 100 illustrated in FIG. 1. As illustrated, the PCB100 still includes the substrate 110 and the insulation region 170created by the plurality of openings 180 formed therethrough. Inaddition, first and second antenna traces 160 a, 160 b are shown formedon opposing faces of the PCB 100. Advantageously, the multiple antennatraces 160 a, 160 b may be employed where electrical circuitry ismounted on both faces of the PCB 100. Also, multiple antenna traces 160a, 160 b may be employed to advantage where the PCB 100 includesmultiple layers, having numerous electrically interconnectionstherethrough.

[0026] Connecting the antenna traces 160 a, 160 b are a plurality ofvias 210. The vias 210 may be formed between the first and secondantenna traces 160 a, 160 b to electrically interconnect them. In anexemplary embodiment, the vias 210 are formed from the same material asthe antenna traces 160 a, 160 b, however other conductive materials mayalso be employed. Although not necessary to practice the presentinvention, multiple antenna traces 160 a, 160 b interconnected withconductive vias 210 provide further enhancement of RF signaltransmission and reception, as those who are skilled in the art willunderstand.

[0027] By providing a PCB that includes openings between an antennatrace and a ground plane, thus removing a substantial portion of thematerial between the two, the present invention provides severalbenefits over the prior art. For instance, the present inventionprovides for increased antenna efficiency. As discussed in detail above,a lossy substrate (for example, an FR-4 PCB) typically has an antennaefficiency of about −2.0 dB, which translates into about 65% radiationefficiency. Forming openings between the antenna trace and the groundplate, thus substantially removing the substrate material therebetweenin accordance to the principles disclosed herein, can increase antennaradiation efficiency to about 90%, with an antenna efficiencyapproaching about −0.5 dB or better. Those skilled in the art willunderstand the dramatic increase in antenna efficiency when employingthe principles of the present invention, even when using a lossysubstrate. Furthermore, those skilled in the art will understand thefurther increases in antenna efficiency that may be achieved byincorporating the present invention into a low-loss substrate.

[0028] In addition, the present invention provides benefits overconventional air antennas mounted over a substrate. For instance,conventional air antennas typically require some human interventionduring the manufacturing process in order to properly mount the antennasabove the substrate. Since an antenna trace according to the presentinvention is still simply etched on the substrate, preferably along withother conductive traces and which is typically an automated process,manufacturing costs may be substantially reduced while obtaining asignificant increase in antenna efficiency. Moreover, since the presentinvention provides for an antenna trace etched on the substrate, thefragile structure, often present with air antennas that are suspendedabove a substrate from only a minimal number of points, is eliminated.

[0029] Forming openings as the insulation region in an antenna structureaccording to the present invention is also relatively simple toincorporate into conventional circuit board manufacturing processes.More specifically, PCBs typically have numerous apertures formed thereinearly in their manufacture. These apertures may later be used formounting the PCB within a larger assembly, for receiving bond pads ofintegrated circuit chips, or even for holding the PCB in certainpositions during latter stages of manufacture. In any event,incorporating the formation of a few more openings early in the PCBmanufacturing process would be extremely simple. As a result,constructing a PCB incorporating the present invention would haveminimal, if any, impact on the time or cost of manufacturing a PCB.Furthermore, this minimal impact to the manufacturing process is thesame whether a single opening is formed between the antenna trace andthe ground plane, or whether a plurality of openings (leaving supportbridges between the two) are formed in the substrate.

[0030] Although the present invention has been described in detail,those skilled in the art should understand that they can make variouschanges, substitutions and alterations herein without departing from thespirit and scope of the invention in its broadest form.

What is claimed is:
 1. An antenna structure, comprising: an antennatrace formed on a substrate proximate a ground plane of said substrate;and an insulation region extending through said substrate and locatedbetween said antenna trace and said ground plane.
 2. The antennastructure recited in claim 1 wherein said insulation region includes aplurality of insulation regions.
 3. The antenna structure recited inclaim 2 wherein each of said insulation regions are separated by aportion of said substrate.
 4. The antenna structure recited in claim 1wherein said insulation region is an opening that extends through saidsubstrate and an insulator of said insulation region is air.
 5. Theantenna structure recited in claim 1 wherein said insulation regionincludes an insulation material selected from a group consisting of: ABSplastic; ceramic; and Teflon.
 6. The antenna structure recited in claim1 wherein said antenna trace includes antenna traces located on opposingsurfaces of said substrate.
 7. The antenna structure recited in claim 1wherein said antenna traces are interconnected by vias extending throughsaid substrate.
 8. A method of manufacturing an antenna structure,comprising: forming an antenna trace on a substrate proximate a groundplane of said substrate; and creating an insulation region extendingthrough said substrate and located between said antenna trace and saidground plane.
 9. The method recited in claim 8 wherein said creatingincludes creating a plurality of insulation regions.
 10. The methodrecited in claim 8 wherein said creating a plurality of insulationregions includes creating a plurality of insulation regions separated bya portion of said substrate.
 11. The method recited in claim 8 whereinsaid creating an insulation region includes creating an opening thatextends through said substrate and wherein an insulator of saidinsulation region is air.
 12. The method recited in claim 11 whereinsaid creating an opening includes drilling a hole in said substrate. 13.The method recited in claim 8 wherein said creating includes creating aninsulation region having an insulation material selected from a groupconsisting of: ABS plastic; ceramic; and Teflon.
 14. The method recitedin claim 8 wherein said forming includes forming antenna traces locatedon opposing surfaces of said substrate interconnected by vias extendingthrough said substrate.
 15. A printed circuit board (PCB), comprising: asubstrate having a ground plane and conductive traces formed thereon;and an antenna structure, including: an antenna trace formed on saidsubstrate proximate said ground plane; and an insulation regionextending through said substrate and located between said antenna traceand said ground plane.
 16. The PCB recited in claim 15 further includingelectrical components mounted on said substrate and interconnectedbetween at least one of said conductive traces and said ground plane toform an operative circuit.
 17. The PCB recited in claim 15 wherein saidinsulation region includes a plurality of insulation regions separatedby a portion of said substrate.
 18. The PCB recited in claim 15 whereinsaid insulation region is an opening that extends through said substrateand an insulator of said insulation region is air.
 19. The PCB recitedin claim 15 wherein said insulation region includes an insulationmaterial selected from a group consisting of: ABS plastic; ceramic; andTeflon.
 20. The PCB recited in claim 15 wherein said antenna traceincludes antenna traces located on opposing surfaces of said substrateinterconnected by vias extending through said substrate.